Improvement of the Linearity of Optical Magnetic Field Sensors.

Optical magnetic field sensors with high linearity and low harmonic distortion were developed. Bi-substituted rare earth iron garnets were prepared by the LPE method for use as the Faraday rotators of these sensors. The linearity error of the sensor output was obtained within ±1.0% for alternating magnetic fields of up to 300 Oe. The sensor optical system has a new converged beam optical system using ball lenses. The linearity of these sensors is very much better than that of sensors using a collimated beam optical system, on account of the use of graded index (GRIN) lenses. Sensors using GRIN lenses have non-linearity, since only the zeroth-order beam diffracted by garnet maze domains is detected. Sensors using ball lenses have high linearity bacause of the detection of diffracted beams up to the second-order. These experimental results agree well with the calculated results.